1. Field of the Invention
The present invention relates to the production of 1,7-octadiene by hydrooligomerizing butadiene.
2. Description of the Prior Art
Linear oligimerization of butadiene is of great interest as a source of C.sub.8 and C.sub.12 unsaturated hydrocarbon intermediates useful for the synthesis of diacids, diesters, diols or diamines. Linear oligomerization of butadiene usually results in the formation of n-octatriene products, and in particular either 1,3,6-octatriene or 1,3,7-octatriene which has a terminal conjugated diene system. The desired dimer for many processes, however, is 1,7-octadiene which only has terminal double bonds. This intermediate would allow the production of products having only terminal functional groups. Butadiene dimerization products with internal double bonds would not be useful to accomplish this, since the desired terminal functional groups would not be obtained selectively in subsequent reactions. Furthermore, the conjugated system in 1,3,7-octatriene is unreactive in may reactions or gives complex reaction mixtures. Thus, a butadiene hydrooligomerization process selective to .alpha.,.omega.-dienes, such as 1,7-octadiens, is desired.
Wright in U.S. Pat. Nos. 3,732,326 and 3,823,199 discloses preparing either 1,6-octadiene or a mixture of 1,6 and 1,7-octadiene by dimerizing butadiene in the presence of formic acid using a palladium acetate catalyst, a phosphine and dimethylformamide, or benzene as a solvent. The yield of and selectively to 1,7-octadiene, however, are unsatisfactorily low. In addition, the catalyst efficiency is quite low.
Wright, in British Pat. No. 1,341,324, discloses dimerizing butadiene with palladium acetate in the presence of formic acid and either triethylamine or morpholine as the solvent. The product is reported to be 1,6-octadiene or a mixture of 1,6 and 1,7-octadiene. The reaction rate and selectivity to 1,7-octadiene, however, are unsatisfactory.
Gardner et al, Tetrahedron Letters No. 2, pp. 163-164, 1972, discloses essentially the same technique as Wright, except for an additional suggestion of carrying out the reaction in a basic solvent.
Roffio et al, Journal of Organometallic Chemistry, 55, 405 (1973) utilize a (PPh.sub.3).sub.2 Pd (C.sub.4 H.sub.6) catalyst in benzene in the presence of formic acid. Roffio et al reported a 75% butadiene conversion, however, only 22% of the product was 1,7-butadiene and the major product was 1,3,7-octatriene.
Accordingly, there continues to exist a need for a process which is capable of dimerizing butadiene to 1,7-octadiene at high yields, high selectivities and good catalyst efficiency.